1. Field of the Invention
This invention relates to polyolefin aerogels, polyolefin microporous materials, methods of making same and articles composed of said aerogels or microporous materials. More particularly, the invention provides microporous poly(dicyclopentadiene) materials prepared by ring-opening metathesis polymerization, polymerization and drying methods of making same and articles composed of the poly(dicyclopentadiene) materials.
2. Background of the Invention
Aerogels, invented in 1931 by Kistler, (Kistler, S. S., “Coherent Expanded Aerogels and Jellies”, Nature, 127, 741 (1931) and “Coherent Expanded Aerogels” J. Physical Chem., 36, 52 (1932)), are formed from a gel by replacing the liquid phase with air. The first aerogels produced by Kistler had silicon dioxide (silica) as the solid phase of the gel structure. Silica gels can be formed via polymerization of silicic acid (Si(OH)4). Aerogels prepared from sol-gel processing with silica oxides have been quite interesting due to their extremely low density, high surface area, and attractive optical, dielectric, thermal and acoustic properties. These excellent properties explain why aerogels have been considered for use in many important applications such as thermal insulations. More detailed description can be found in the following references: LeMay et al., “Low-Density Microcellular Materials”, MRS Bulletin, December 1990, p. 19-44, and D. Schaefer, “Structure of mesoporous aerogels”, MRS Bulletin, April 1994, p. 49-53.
The ambient pressure drying process is called the “xerogel” process, and results organic and inorganic based wet gel with many physical properties which differ from aerogels. For example, U.S. Pat. No. 5,478,867 disclosed a microporous isocyanate-based xerogel composition and method of its preparation using a vacuum oven. However, this ambient pressure drying process generally shows more shrinkage and damage due to surface tension forces during drying. Moreover, the drying time for xerogels is relatively very long.
The primary approach to making aerogels is to dry the gel matrix in a supercritical fluid medium. Kistler used a supercritical alcohol process to dry the gel matrix. Such processes, though successful, are energy intensive due to higher critical points of alcohols. Another method is to use supercritical carbon dioxide, which has a relatively lower critical point. During supercritical drying, the temperature and the pressure are increased beyond the critical point where the phase boundary between the liquid and vapor phase disappears. Once the critical point is passed, there is no distinction between the liquid and vapor phase and the solvent can be removed without introducing a liquid-vapor interface, capillary pressure, or any associated mass transfer limitations. Liquid CO2 is generally used as the supercritical extraction fluid because the process can be performed near ambient temperature. A good description of supercritical drying technology may be found in a recent process patent, U.S. Pat. No. 6,670,402, which discloses a rapid aerogel production process utilizing a unique supercritical fluid-pressure modulation technique. An example of supercritical drying of organic aerogel can also be found in U.S. Pat. No. 5,962,539, which discloses a process and equipment for drying a polymeric aerogel in the presence of a supercritical fluid.
Although silica aerogels demonstrate many unusual and useful properties, they are inherently fragile, brittle, and hydrophilic. There have been several attempts at overcoming weakness and brittleness issues in silica aerogels. Development of the flexible fiber-reinforced silica aerogel composite blanket is one of the promising approaches. For example, U.S. Pat. No. 6,068,882 discloses forming aerogels interstitially within a fiber matrix. However, for certain applications requiring durability under dynamic use conditions such as in spacesuits, the silica aerogel blankets still exhibit durability problems related to dust generation and thermal performance degradation due to the fragile nature of the aerogel. Organically-treated silica aerogels demonstrate much improved impact and flexural strength. More details on such hybrid silica aerogels obtained by co-polymerization with an organic compound can be found in the following references: Leventis et al, “Nanoengineering Strong Silica Aerogels”, Nano Letters, 2, 957, (2002), and Zhang et al, “Isocyanate cross-linked silica, structurally strong aerogels” Polymer Preprint, 44, 35 (2003). However, these materials are still very brittle (i.e., not less fragile) and generate dust. More flexible aerogels than silica aerogels have been reported, and are referred to as organically-modified silica aerogel, or Ormosil, by Schmidt H., “New type of non-crystalline solids between inorganic and organic materials”, J Non-Cryst. Solids, 73, 681 (1985), or as Aeromosil by Kramer et al., “Organically Modified Silicate Aerogel, Aeromosil” Mat. Res. Soc. Symp. Proc. 435, 295 (1996). However, these are still weak, generate dust when handled, and are not durable due to the inherently fragile nature of the predominant silica aerogel matrix.
The unique porous nanostructure was also reported in organic and carbon based aerogels. A good description for organic aerogels can be found in Pekala and Schaefer, “Structure of organic aerogels. 1. Morphology and Scaling”, Macromolecules 26, 5487 (1993). Kistler first prepared organic aerogels based on natural products and their derivatives. Pekala and co-workers developed several organic aerogels. More details can be found in the following references: Polym. Preprints, 29, 204 (1988), Polym. Preprints 30, 221 (1989), U.S. Pat. Nos. 4,873,218, 4,997,804, U.S. Pat. Nos. 5,081,163, 5,086,085, U.S. Pat. No. 5,476,878. Biesmans et al. describes polyurethane aerogels, and/or their pyrolyzed carbon-aerogel counterparts. Details on this can be obtained from the following references: Biesmans et al., “Polyurethane based organic aerogels' thermal performance” J Non-Cryst. Solids, 225, 36 (1998), Biesmans et al., “Polyurethane based organic aerogels and their transformation into carbon aerogels” J Non-Cryst. Solids, 225, 64 (1998), and Rigacci A., et al., “Preparation of polyurethane-based aerogels and xerogels for thermal superinsulation”, J Non-Cryst. Solids, 350, 372 (2004). U.S. Pat. Nos. 5,478,867, 5,484,818, 5,942,553, 5,869,545, and 5,990,184 describe polyisocyanurate-based organic xerogels and aerogels and their preparation methods. However, since these polyisocyanurate or polyurethane based materials were mostly tailored for xerogels or highly crosslinkable systems and constituent components suitable for carbon aerogel and vacuum panel applications, they are very brittle and stiff. Also, such polyisocyanurate or polyurethane based aerogel system is slowly gelled at ambient conditions, which is a major economic disadvantage in production. In addition, polyurethane based aerogels previously described show high thermal conductivity values. Recently, a very strong and less fragile organic aerogel was introduced, and more details can be obtained from following references, Tan et al, “Organic Aerogels with Very High Impact Strength” Advanced. Materials, 13, 644 (2001) and Zhang G. et al., “Isocyanate-crosslinked silica aerogel monoliths: preparation and characterization”, J Non-Cryst. Solids, 350, 152 (2004). Although they significantly improved mechanical properties and obtained less fragile aerogels, they were still very rigid and brittle when compared with the materials of the present inventions. These materials would not be suitable for certain applications requiring exceptional flexibility and durability, such as spacesuit, military and civilian apparels, tents, shoes, and gloves.
Dicyclopentadiene (DCPD), produced by heating crude oil products, results from a facile Diels-Alder dimerization of cyclopentadiene (CP monomer). The main interest in the DCPD monomer is that it can be used to produce a range of different macromolecular architectures, from purely linear to highly cross-linked polymers. DCPD is also an economically interesting monomer since it is a byproduct in the petrochemical industry such as ethylene manufacture and thus, is cheap and readily available. Poly DCPD has been used, to produce many products, ranging from high quality optical lenses to flame retardants for plastics, hot melt adhesives, and other injection molding products. Other applications include uses as a chemical intermediate in the manufacture of insecticides, a hardener and dryer in linseed and soybean oil, and in the production of several polymeric systems such as ethylene propylene diene monomer (EPDM) and elastomers as a co-monomer, metallocenes, varnishes, and paints. DCPD resins have been formulated to make tough thermoset materials via Ring Opening Metathesis Polymerization (ROMP) reactions, examples of which can be found in U.S. Pat. No. 4,400,340, U.S. Pat. No. 4,469,809, and U.S. Pat. No. 6,020,443. PolyDCPD produced via the ROMP reaction may be post cured to increase the degree of the cross-linking of the polyDCPD material. PolyDCPD is a tough, rigid and low-cost thermoset polymer with excellent mechanical, chemical and physical properties such as: high modulus, low viscosities, extraordinary tensile and impact strength, good physical and mechanical durability at lower temperatures, excellent chemical resistance, and excellent hydrophobicity. In addition, the polymer surface and network can be easily chemically modified via reaction with the many pendant unsaturated double bonds resulting from the ROMP reaction.
PolyDCPD based aerogel monoliths and composites (including fiber-reinforced composites and hybrid material composites) have not been described before. The present invention relates to PolyDCPD based aerogel monoliths and composites, methods for their preparation and applications.